Global Climate Model (GCM)

Khaled KheireldinProfessor, PE

Director Climate Change Research Institute

Seminar

Presentation Outline

• Overview of the Climate System

• Modeling of Climate Change

• General Circulation Model (GCM)

• IPCC SRES Scenarios

• Regional Climate Model (RCM)

• Climatic Modeling at BUET

Climate Models

• Climate models are computer-based simulations that use mathematical formulas to re-create the chemical and physical processes that drive Earth’s climate. To “run” a model, scientists divide the planet into a 3-dimensional grid, apply the basic equations, and evaluate the results.

• Atmospheric models calculate winds, heat transfer, radiation, relative humidity, and surface hydrology within each grid and evaluate interactions with neighboring points. Climate models use quantitative methods to simulate the interactions of the atmosphere, oceans, land surface, and ice.

General Circulation Model (GCM)• General Circulation Models (GCMs) are a class of computer-

driven models for weather forecasting, understanding climate and projecting climate change, where they are commonly called Global Climate Models.

• Three dimensional GCM's discretise the equations for fluid motion and energy transfer and integrate these forward in time. They also contain parameterizations for processes -such as convection - that occur on scales too small to be resolved directly.

• Atmospheric GCMs (AGCMs) model the atmosphere and impose sea surface temperatures. Coupled atmosphere-ocean GCMs (AOGCMs, e.g. HadCM3, EdGCM, GFDL CM2.X, ARPEGE-Climate) combine the two models.

GCM typical horizontal resolution of between 250 and 600 km, 10 to 20 vertical

layers in the atmosphere and sometimes as many as 30 layers in the oceans.

Heart of Climate Model

Complexity of GCM

Hardware Behind the Climate Model

• Geophysical Fluid Dynamics Laboratory

Special Report on Emissions

Scenarios (SRES)

• The Special Report on Emissions Scenarios (SRES) was a report prepared by the Intergovernmental Panel on Climate Change (IPCC) for the Third Assessment Report (TAR) in 2001, on future emission scenarios to be used for driving global circulation models to develop climate change scenarios.

• It was used to replace the IS92 scenarios used for the IPCC Second Assessment Report of 1995. The SRES Scenarios were also used for the Fourth Assessment Report (AR4) in 2007.

SERS Emission Scenarios

• A1 - a future world of very rapid economic growth, global population that peaks in mid-century and declines thereafter, and the rapid introduction of new and more efficient technologies. Three sub groups: fossil intensive (A1FI), non-fossil energy sources (A1T), or a balance across all sources (A1B).

• A2 - A very heterogeneous world. The underlying theme is that of strengthening regional cultural identities, with an emphasis on family values and local traditions, high population growth, and less concern for rapid economic development.

• B1 - a convergent world with the same global population, that peaks in mid-century and declines thereafter, as in the A1 storyline.

• B2 - a world in which the emphasis is on local solutions to economic, social and environmental sustainability.

• Representative Concentration Pathways (RCP) 4.5

Low-medium emissions increasing scenario

• Representative Concentration Pathways (RCP) 8.5

Fossil fuel intensive scenario

RCP 8.5

RCP 4.5

Global Climate Simulation Scenarios

RCP:20052100

Source: http://stratus.astr.ucl.ac.be/textbook/pdf/Chapter_6.pdf

Arctic Sea Ice Prediction using

community climate system model

Arctic Sea Ice in

2040Arctic Sea Ice in

2000

Prediction of Global Warming

• Figure shows the distribution of warming during the late 21st century predicted by the HadCM3 climate model. The average warming predicted by this model is 3.0 °C.

Prediction of Temperature increase

Prediction of Sea level rise

Regional details of Climate Change

Regional Climate modeling

• An RCM is a tool to add small-scale detailed information of future climate change to the large-scale projections of a GCM. RCMs are full climate models and as such are physically based and represent most or all of the processes, interactions and feedbacks between the climate system components that are represented in GCMs.

• They take coarse resolution information from a GCM and then develop temporally and spatially fine-scale information consistent with this using their higher resolution representation of the climate system.

• The typical resolution of an RCM is about 50 km in the horizontal and GCMs are typically 500~300 km

RCM can simulate cyclones and

hurricanes

Regional Climate change modeling

• PRECIS regional climate modeling is now running in Climate change study cell at IWFM,BUET.

• Uses LBC data from GCM (e.g. HadCM3).

• LBC data available for baseline, A2, B2, A1B scenarios up to 2100.

• Predictions for every hour. Needs more than 100 GB free space.

Domain used in PRECIS experiment

Topography of Experiment Domain

Zoom over BangladeshSimulation Domain = 88 x 88

Resolution = 0.44 degree

Predicted Change of Mean

Temperature (0C) using A1B

2050 2090

Baseline = 2000

Predicting Maximum Temperature

using A2 Scenarios

[Output of PRECIS model using SRES A2 scenario]

[Output of PRECIS model using SRES A2 scenario]

Predicting Minimum Temperature

using A2 Scenarios

Change of Mean Rainfall (mm/d)

using A1B Scenarios

2050 2090

Baseline = 2000

Predicting Rainfall using A2

Scenarios

[Output of PRECIS model using SRES A2 scenario]

Conclusions

Global Circulation Models are the only way to predict thefuture climate.

It needs many verifications and ground truth based onhistorical data.

42 GCM Models are Available till today from manycountries.

Through the information of the GCMsw we have the opportunity to conduct climate change adaptation.

Thank you